This application is based upon and claims priority of Japanese Patent Application No. 2002-76178, filed in Mar. 19, 2002, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device having a nonvolatile memory (FeRAM: Ferroelectric Random Access Memory) in which ferroelectric material is employed as the dielectric film of the capacitor and a method of manufacturing the same.
2. Description of the Prior Art
In the FeRAM, the cell area will be more reduced in response to the demand for the higher integration in the future. If the cell area is reduced in such a way, the interval between neighboring capacitors is also shortened and the wiring interval is also narrowed accordingly. It is general that the spaces between the capacitors and the spaces between the wirings are buried with the insulating film. In this case, if the higher integration makes progress as above, the insulating film having the good filling property not to form the cavity (also called as the blowhole or the void) between the capacitors must be employed as such insulating film.
As the insulating film having the good filling property, the film that is formed by the high density plasma CVD (HDPCVD) method is known in the prior art.
The insulating film that is formed by the HDPCVD method can be shown in FIG. 1 of Patent Application Publication (KOKAI) 2001-210798, for example. In this Publication, it is disclosed in the paragraph number 0042 that the HDP oxide can be used as the insulating film 134 for covering the capacitor in FIG. 1.
Similarly, in Patent Application Publication (KOKAI) 2001-230382, it is disclosed in the paragraph number 0084 that the HDP oxide can be used as the insulating film 408 for covering the capacitor in FIG. 4a. 
Meanwhile, SiH4 is used in general as the film forming gas in the HDPCVD method. This SiH4 is decomposed during the film formation to generate the hydrogen. Thus, there is given the chance that the ferroelectric film of the capacitor is exposed to the hydrogen.
However, if the ferroelectric film is exposed to the reducing material such as the hydrogen or the like, the deterioration of the ferroelectric characteristic is brought about. Therefore, any measure for preventing such deterioration is needed.
In the usual plasma CVD method that is not the HDPCVD method, as the method of isolating the ferroelectric film from the hydrogen, the structure for covering the capacitor with the insulating film made of the metal oxide, e.g., the alumina (Al2O3) film, is known. Such structure is disclosed in Patent Application Hei 11-215600, Patent Application Publication (KOKAI) 2001-44375, Patent Application Publication (KOKAI) Hei 6-29098, and Japanese Patent No. 3056973.
However, it is made apparent by the inventors of the present invention that, in the HDPCVD method, this alumina film is not enough to block the hydrogen and thus the deterioration of the ferroelectric film is caused by the hydrogen.
It is an object of the present invention to provide a semiconductor device capable of preventing deterioration of a ferroelectric film in a capacitor when an insulating film for covering the capacitor is formed, and a method of manufacturing the same.
The above problems can be solved by providing a semiconductor device manufacturing method which comprises the steps of forming a first insulating film over a semiconductor substrate; forming a first conductive film, a ferroelectric film, and a second conductive film sequentially on the first insulating film; forming an upper electrode of a capacitor by patterning the second conductive film; forming a dielectric film of the capacitor by patterning the ferroelectric film; forming a lower electrode of the capacitor by patterning the first conductive film; forming a first capacitor protection insulating film covering the dielectric film and the upper electrode; forming a second capacitor protection insulating film, which covers the first capacitor protection insulating film, by a chemical vapor deposition method in a state that a bias voltage is not applied to the semiconductor substrate; and forming a second insulating film on the second capacitor protection insulating film by the chemical vapor deposition method in a state that the bias voltage is applied to the semiconductor substrate.
Next, advantages of the present invention will be explained hereunder.
According to the present invention, the first capacitor protection insulating film for covering the capacitor dielectric film and the upper electrode is formed. Then, the second capacitor protection insulating film is formed on the first capacitor protection insulating film in the state that the bias voltage is not applied to the semiconductor substrate, and then the second insulating film is formed in the state that the bias voltage is applied.
Because the second insulating film is formed in the state that the bias voltage is applied, the electric field is concentrated onto the shoulder portion of the capacitor, for example, and then the sputter ions are pulled into the shoulder portion by this electric field. Accordingly, the deposition and the sputter of the film are executed simultaneously at the shoulder portion, so that it can be prevented that the film is formed thick on the shoulder portion. As a result, the film thickness on the side surfaces of the capacitor can be made even, and thus the second insulating film having the good filling property can be formed between the capacitors of high aspect ratio. Since the filling property is good, the cavity is not formed in the second insulating film between the capacitors even when the interval between the capacitors is narrowed with the progress of the higher integration.
In addition, even when the second insulating film is formed in the state that the bias voltage is applied, the collision energy of the sputter ions and other ions is absorbed by the second capacitor protection insulating film to decrease its moving speed. As a result, the ions can be blocked by the underlying first capacitor protection insulating film, and thus the capacitor dielectric film can be prevented from being deteriorated by the ions.
Further, the second capacitor protection insulating film is formed in the state that the bias voltage is not applied to the semiconductor substrate. Therefore, the capacitor dielectric film can be prevented from being deteriorated in the film formation.
Similarly, when the first capacitor protection insulating film is formed in the state that the bias voltage is not applied to the semiconductor substrate, the deterioration of the capacitor dielectric film in the film formation can be prevented.
Also, since the second capacitor protection insulating film is formed by the chemical vapor deposition method using the reaction gas containing TEOS, the coverage of the second capacitor protection insulating film can be improved, and thus the collision ions can be absorbed at the upper portion and the side portions of the capacitor uniformly. Further, since hydrogen, which is reducing substance, is hard to generate from TEOS in contrast to SiH4, there is no chance that the capacitor is deteriorated by the hydrogen.
In this case, when the second insulating film is formed by the chemical vapor deposition method using the reaction gas containing any one of SiH4, Si2H6, Si3H8, and SiCl4, an amount of carbon contained in the second capacitor protection insulating film becomes larger than an amount of carbon contained in the second insulating film.
Further, it is preferable that the above first capacitor protection insulating film be formed to have a double-layered structure consisting of the lower protection insulating film, which covers the dielectric film and the upper electrode of the capacitor, and the upper protection insulating film, which is formed on the lower protection insulating film and the first insulating film. According to this, since the capacitor and the first insulating film are covered continuously with the upper protection insulating film, it is possible to prevent the entering of the reducing substance such as the hydrogen, or the like into the capacitor dielectric film via the first insulating film.
Besides, where the capacitor is formed in plural, if the total film thickness of the first capacitor protection insulating film and the second capacitor protection insulating film is set smaller than half of the minimum interval among a plurality of upper electrodes, the spaces between the capacitors can be filled desirably, with the second insulating film between the capacitors free from cavity.
Moreover, it is preferable that the film thickness of the second insulating film be set thicker than the total film thickness of the capacitor upper electrode, the capacitor dielectric film, and the capacitor lower electrode but thinner than the film thickness that is obtained by adding 1 xcexcm to the total film thickness. According to this, while suppressing maximally the deterioration of the capacitor dielectric film due to ions that are generated in the film formation of the second insulating film, the spaces between the capacitors can be filled with the second insulating film.
Also, where the surface of the second insulating film is planarized by the polishing, the third insulating film is formed on the second insulating film before the polishing, and then the second and third insulating films are polished together. Therefore, the film thickness to be polished can be increased and also the distribution of the film thickness after the polishing can be set uniformly.